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compost feasibility shows Dry AD most affordable over 20 years
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by Cedric de La Beaujardiere, Barron Park,
on Feb 26, 2011
The Compost Financial Feasibility Study's Preliminary Cost Analysis Summary indicates (Web Link
YEAR-1 ...| YEAR-20 ...| 20-YEAR TOTAL | PROJECT/FINANCING OPTION
$ 68/ton ....| $118/ton ...| $71 million ..........| Truck food & yard to Gilroy, Incinerate sewage
$112/ton ...| $106/ton ...| $91 million ..........| Dry AD: private financing/private operation
$ 81/ton ....| $ 81/ton ....| $67 million ..........| Dry AD: public financing/private operation
$ 62/ton ....| $ 65/ton ....| $52 million ..........| Dry AD: City receives 30% in grants worth $12M
This shows that, over a 20 year period, the public financing of local Dry Anaerobic Digestion is $4 million more affordable than sending our wastes away. With a 30% grant, we save the rate-payers $19 million, which comes out to about $1 million a year in savings through handling our wastes locally.
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Posted by Cedric de La Beaujardiere
a resident of Barron Park
on Feb 27, 2011 at 1:07 am
Cedric de La Beaujardiere is a registered user.
Thanks for your questions. Sorry in advance that my answers tend to be so long-winded.
First, for clarity, my post was an excerpt from my longer post in response to an article and its comments at Web Link. I actually posted here only because my table originally lost its formatting, so I wanted to post it somewhere else and make sure i had the column alignment right.
To get to your questions, if there was an alternative for handling all of our organics (yard trimmings, food scraps, and sewage) at much less than $62/ton (which is unlikely), yes, I would be impressed, and it would be a logical choice from a purely fiscal perspective. I would personally take a more systems-level perspective and consider whether the solution emitted more or less Green House Gases, or had other adverse impacts. So, for instance, to indefinitely continue our current sewage incineration is neither fiscally nor environmentally responsible.
In your hypothetical scenario, "if that choice would also solve many more issues than anaerobic digestion does", and if it was a realistic solution with reasonable chance of success, or a means of testing it out, then yes, I would likely think such a solution was awesome and support it.
I think a viable solution better than Anaerobic Digestion (AD) is unlikely, based on my experience serving on the city's 7-month Compost Task Force. Asked to study options for the city, we ended up recommending Dry Anaerobic Digestion because of its promise as a cost-effective and ecologically-sound solution for the city's organics waste management. So far, the independent, 3rd-party feasibility study supports this conclusion.
However, using Wet AD to digest our sewage and food together, and then compost the digestate with yard trimmings could also be viable, and members of the Palo Alto Green Energy Initiative (www.PAGreenEnergy.org) have asked that this also be considered in the feasibility study. Unlike Dry AD, Wet AD is proven for sewage, a point in its favor. On the downside, Wet AD may have more trouble with food scraps in its fluid pumps, and Wet AD uses more energy to move all that extra water around, so it may produce less net energy than Dry AD. These downsides are why the Compost Task Force recommended Dry rather than Wet AD, for the handling of food, yard, and sewage.
Regarding handling the municipal organics, the cost varies by material and treatment option (data from Web Link, in spreadsheet link labelled "Energy/Compost Preliminary Cost Estimate/Low Cost Range/Electricity", tab "2&3"):
- Yard trimmings are the cheapest and easiest to handle, the draft feasibility study shows yard-trimmings handling costing $32/ton in year-one (2015) and $49/ton in year-twenty (the increase due purely to inflation, and does not include the rising cost of fuel).
- Food scraps are more difficult to handle, and for 2015, composting is estimated at $82/ton, while sending it to GreenWaste's as yet unbuilt San Jose Dry AD facility is roughly estimated to be $99/ton.
- Sewage solids (AKA Biosolids) are currently incinerated and priced at $90/ton for 2015. Beyond inflation and rising prices for natural gas, this price should go up significantly to keep the incinerator running past it's remaining 10-year life span and through increased regulatory controls like limits on mercury emissions.
- Landfilling is not cheap either, at $53/ton for 2015 (from "Inputs" tab).
Averaged for all three inputs and their quantities, the cheapest non-local-AD and current default option for the city is $68/ton in 2015 (to compost food & yard in Gilroy, & Incinerate sewage). This goes up to $118/ton in year-20, but this is probably an under-estimate of the true cost for the reasons I stated above.